Chemistry Reference
In-Depth Information
TABLE 4.10. Kinetics of the Oxidation of Amino Acids with O
3
at Ambient
Temperature
k
(O
3
)
a
O
3
demand
b
k
(AA)
c
Amino
Acids
p
K
a2
(/M/s)
(mol/mol)
(/M/s)
t
1/2
(AA)
d
1.0 × 10
3
1.5 × 10
2
Ala
9.87
6.7
217 seconds
Arg
9.04
5.3 × 10
3
9.1
5.8 × 10
2
58 seconds
Asn
8.72
8.0 × 10
3
7.3
1.1 × 10
3
30 seconds
Asp
9.82
6.2 × 10
2
4.3
1.4 × 10
2
230 seconds
glu
9.47
8.8 × 10
2
3.8
2.3 × 10
2
144 seconds
gln
9.13
1.9 × 10
3
-
-
-
gly
9.78
3.5 × 10
3
5.4
6.5 × 10
2
52 seconds
1.7 × 10
4
1.7 × 10
3
His
9.18
9.7
19 seconds
9.8 × 10
2
Ile
9.76
-
-
-
Leu
9.74
9.6 × 10
2
5.7
1.7 × 10
2
197 seconds
Lys
8.95
3.5 × 10
3
9.3
3.7 × 10
2
89 seconds
Met
9.28
3.8 × 10
6
7.2
5.3 × 10
5
63 millisecond
Phe
9.31
1.9 × 10
4
9.2
2.1 × 10
3
16 seconds
Pro
10.6
1.1 × 10
4
8.3
1.3 × 10
3
25 seconds
Ser
9.21
8.0 × 10
3
9.7
8.2 × 10
2
41 seconds
3.6 × 10
3
3.7 × 10
2
Thr
9.1
9.8
91 seconds
Trp
9.39
7.0 × 10
6
12.9
5.4 × 10
5
61 millisecond
Tyr
9.11
-
13.4
-
-
Val
9.74
1.2 × 10
3
-
-
-
a
calculated at pH 8.0 from the values of
k
HA
and
k
A
given in Pryor et al. [223].
b
Reported by Hureiki et al. [230] (pH 8).
c
calculated compound reaction rate constant at pH 8.
d
Assuming [O
3
] = 1 mg/L (pH 8).
Adapted from Sharma and graham [15].
the final product of ozonolysis [235]. However, a recent study yielded a com-
pound in which three oxygen atoms were added to His. A proposed structure
of a compound as the only oxidized product is shown in Figure 4.16 [239]. Two
studies of the ozonolysis of Trp have indicated the formation of NFK as the
major oxidized product (Fig. 4.16) [225, 239]. The ozonolysis of Tyr yielded
3,4-dihydroxyphenylalanine (DOPA) (Fig. 4.16) [225, 233]. Significantly, the
ozonolysis of peptides containing Met (gly-gly-Phe-Met, Tyr-gly-gly-Phe-
Met), His (His-Leu, gly-His-Lys), and Trp (Lys-Trp-Lys) formed products that
were in agreement with the expected products from the oxidation of free
amino acids by O
3
[239]. A study on the degradation of Tyr-gly-gly (2.5 mg/L
total organic carbon) by O
3
in the presence of bicarbonate buffer at pH 7.2
showed 0.26 mg of consumed O
3
achieved complete removal of the Tyr residue;
however, only 23.3% of the gly residue was removed [256].
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